engine coolant fans not functioning
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From: Palm City FL
engine coolant fans not functioning
My 1996 overheated while idling and I realized the coolant fans never kicked on. My question is after reading the troubleshooting guide in the GM manual they stated to turn the fans on via scantool codes. I have a scantool, but I do not know the command to send to the ECU to turn on fan 1 or 2 manually? I think the ECT sensor maybe bad, however I would like to make sure the fans are good!
Burning Brakes
Joined: Sep 2010
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Turn the air conditioner on and both fans will operate at high speed if functioning as designed. This will let you know if the fans are OK.
What temp did your cooling system reach when it overheated? If I recall correctly, for 1996 (with the air conditioner OFF), the fans don't operate at low speed until 228 degrees F.
What temp did your cooling system reach when it overheated? If I recall correctly, for 1996 (with the air conditioner OFF), the fans don't operate at low speed until 228 degrees F.
Last edited by MissileDoc; Aug 28, 2011 at 08:31 PM.
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Joined: Jul 2011
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From: Palm City FL
Turn the air conditioner on and both fans will operate at high speed if functioning as designed. This will let you know if the fans are OK.
What temp did your cooling system reach when it overheated? If I recall correctly, for 1996 (with the air conditioner OFF), the fans don't operate at low speed until 238 degrees F.
What temp did your cooling system reach when it overheated? If I recall correctly, for 1996 (with the air conditioner OFF), the fans don't operate at low speed until 238 degrees F.
Burning Brakes
Joined: Sep 2010
Posts: 937
Likes: 385
In your FSM, take a look at page 6-639, Electric Cooling Fan Diagnosis, Circuit Description to see how the cooling fans are supposed to operate. Also, look at the electrical diagram on page 6-290.
Compare the wiring colors in the diagram to the wires on your three relays to find which relay is number 1, 2 and 3.
Relay number one will recieve a ground on wire 335 (dark green in color) from the PCM when the temp reches 228 degrees F (this is how my '96 works also). This will cause both fans to operate in low speed. You need to determine if the relay number one coil is becoming energized when the PCM is allowing this ground. I did a voltage check on the left cooling fan wiring connector light blue wire to see if the contact was closing to power the fan at the proper temp.
You can follow the fan low speed 12 vdc power path from relay number one to the left cooling fan motor, through relay number three's 87A contact to the S123 connector, through the right cooling fan motor finally to the motor ground.
Above all, be safe when troubleshooting.
Long message, but I hope it helps.
Compare the wiring colors in the diagram to the wires on your three relays to find which relay is number 1, 2 and 3.
Relay number one will recieve a ground on wire 335 (dark green in color) from the PCM when the temp reches 228 degrees F (this is how my '96 works also). This will cause both fans to operate in low speed. You need to determine if the relay number one coil is becoming energized when the PCM is allowing this ground. I did a voltage check on the left cooling fan wiring connector light blue wire to see if the contact was closing to power the fan at the proper temp.
You can follow the fan low speed 12 vdc power path from relay number one to the left cooling fan motor, through relay number three's 87A contact to the S123 connector, through the right cooling fan motor finally to the motor ground.
Above all, be safe when troubleshooting.
Long message, but I hope it helps.
Last edited by MissileDoc; Aug 29, 2011 at 05:32 PM.
Thread Starter
Advanced
Joined: Jul 2011
Posts: 84
Likes: 0
From: Palm City FL
In your FSM, take a look at page 6-639, Electric Cooling Fan Diagnosis, Circuit Description to see how the cooling fans are supposed to operate. Also, look at the elecrtical diagram on page 6-290.
Compare the wiring colors in the diagram to the wires on your three relays to find which relay is number 1, 2 and 3.
Relay number one will recieve a ground on wire 335 (dark green in color) from the PCM when the temp reches 228 degrees F (this is how my '96 works also). This will casuse both fans to operate in low speed. You need to determine if the relay number one coil is becoming energized when the PCM is allowing this ground. I did a voltage check on the left cooling fan wiring connector light blue wire to see if the contact was closing to power the fan at the proper temp.
You can follow the fan low speed 12 vdc power path from relay number one to the left cooling fan motor, through relay number three's 87A contact to the S123 connector, through the right cooling fan motor finally to the motor ground.
Above all, be safe when troubleshooting.
Long message, but I hope it helps.
Compare the wiring colors in the diagram to the wires on your three relays to find which relay is number 1, 2 and 3.
Relay number one will recieve a ground on wire 335 (dark green in color) from the PCM when the temp reches 228 degrees F (this is how my '96 works also). This will casuse both fans to operate in low speed. You need to determine if the relay number one coil is becoming energized when the PCM is allowing this ground. I did a voltage check on the left cooling fan wiring connector light blue wire to see if the contact was closing to power the fan at the proper temp.
You can follow the fan low speed 12 vdc power path from relay number one to the left cooling fan motor, through relay number three's 87A contact to the S123 connector, through the right cooling fan motor finally to the motor ground.
Above all, be safe when troubleshooting.
Long message, but I hope it helps.
The FSM stated that the ECT needed to be replaced, but your suggestions are great and appreciate your advice.
